Samsung is suspected of providing tens of millions of dollars in money and favours to President Park Geun-hye and her jailed friend Choi Soon-sil in exchange for government support of a merger deal between two Samsung affiliates in 2015.

The merger helped Lee, the billionaire vice chairman of technology giant Samsung Electronics, promote a father-to-son transfer of leadership and wealth at the group.

The bribery allegation surfaced as authorities expanded investigations into a political scandal that led to Park's parliamentary impeachment.

Prosecutors accuse Park of letting Choi pull government strings from the shadows and extort money from Samsung and other big companies.

Prosecutors planned to question Lee over new findings they made in the past few weeks and may consider requesting an arrest warrant for him again, according to prosecution spokesman Lee Kyu-chul.

While entering a prosecution office, Lee Jae-yong told reporters that he would faithfully undergo questioning.

Prosecutors had sought to arrest Lee when they summoned him last month, but the Seoul Central District Court ruled there was not enough evidence to justify Lee's arrest at that point.

Moon Hyung-pyo, the country's former health minister, has been indicted on charges that he pressured the National Pension Service to support the Samsung merger even though the fund's stake in one of the companies lost an estimated hundreds of millions of dollars in value.

Park's lawyers scrapped plans to let authorities question Park in person last week to protest media leaks about the timing and location of her interview.

The moves come as the country's Constitutional Court deliberates on whether to formally end her rule and trigger an early election to choose her successor.